This book includes an editorial and 12 research papers on micromixers collected from the Special Issue published in Micromachines. The topics of the papers are focused on the design of micromixers, ...their fabrication, and their analysis. Some of them proposed novel micromixer designs. Most of them deal with passive micromixers, but two papers report studies on electrokinetic micromixers. Fully three-dimensional (3D) micromixers were investigated in some cases. One of the papers applied optimization techniques to the design of a 3D micromixer. A review paper is also included and reports a review of recently developed passive micromixers and a comparative analysis of 10 typical micromixers.
A novel spiral micromixer with sinusoidal channel walls was designed to enhance the mixing index in the low to intermediate Reynolds number range (1 < Re < 100). To analyze the fluid flow, a set of ...numerical simulations were performed using the finite‐difference method. The microchip was fabricated from polydimethylsiloxane, employing the soft‐lithography technique. The degree of mixing was increased by 99.11 % when using the proposed micromixer, compared to 59.44 % for a simple spiral micromixer. The introduced microchannel drastically reduced the mixing length, increasing the mixing index of a 0.5‐loop spiral‐sinusoidal microchannel compared to that of the simple spiral microchannel with 1.5 loops. The mixing index of the 3‐loop mixer was higher than that of the microchannel with 1.5 loops, and its pressure drop was increased.
A novel spiral micromixer with sinusoidal channel walls, fabricated from polydimethylsiloxane, is proposed to enhance the mixing index in the low and intermediate Reynolds number ranges. A set of numerical simulations were performed, showing that the degree of mixing is increased by 99.11 %, while this value is 59.44 % for a simple spiral micromixer.
•Investigated nature-inspired micromixers based on Murray's law.•Employed ANSYS CFX to assess the mixing impact of asymmetric bifurcations.•Compared the performance of asymmetric and symmetric ...bifurcated micromixers.•Anticipated disturbances but observed no improvement in mixing efficiency.•Achieved good mixing in the 0.8 rdv micromixer.
In this novel study, nature inspired biomimetic based micromixers with asymmetric bifurcation are designed and analysed, incorporating daughter vessel ratios (rdv) of 0.6, 0.7, 0.8, and 0.9 based on Murray's law. By leveraging the concept of Murray's law, four micromixers were developed to address the challenges of mixing at the microscale. Achieving efficient mixing is crucial for microfluidic devices in bioengineering and chemical applications. In this work, we examined asymmetric and symmetric bifurcated micromixers across a wide range of Reynolds numbers, from 0.01 to 300. The results demonstrate that almost all the Reynolds number are better handled by the asymmetric bifurcated micromixer having rdv=0.8. The unbalanced collision of the two fluid streams in this configuration promotes enhanced mixing performance. In contrast, the symmetric micromixer, which lacks such imbalances, shows comparable mixing performance across different Reynolds numbers, except for a Reynolds number of 10. In some cases of asymmetric bifurcated micromixers, inadequate mixing occurred due to the dominance of the larger daughter vessel, impeding the participation of the smaller one in the mixing process. The research reveals that asymmetric bifurcated micromixers with rdv=0.8 are exhibit slightly higher mixing efficiency than symmetric bifurcated micromixers with rdv=1.0.
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Micromixers are critical components in the lab-on-a-chip or micro total analysis systems technology found in micro-electro-mechanical systems. In general, the mixing performance of the micromixers is ...determined by characterising the mixing time of a system, for example the time or number of circulations and vibrations guided by tracers (i.e., fluorescent dyes). Our previous study showed that the mixing performance could be detected solely from the electrical measurement. In this paper, we employ electromagnetic micromixers to investigate the correlation between electrical and mechanical behaviours in the mixer system. This work contemplates the “anti-reciprocity” concept by providing a theoretical insight into the measurement of the mixer system; the work explains the data interdependence between the electrical point impedance (voltage per unit current) and the mechanical velocity. This study puts the electromagnetic micromixer theory on a firm theoretical and empirical basis.
In the last decade there has been an exponential increase in microfluidic applications due to high surface-to-volume ratios and compactness of microscale devices, which makes them attractive ...alternatives to conventional systems. The continuing growing trends of microfluidic highlights the importance to understand the mechanism and fundamental differences involved in fluid flow and mixing at microscale. In the present article, the experimental research efforts in the area of microscale single-phase fluid flow and issues associated with investigations at microscale flow have been summarized. The experimental data are being analyzed in terms of friction factor, laminar-to-turbulent transition, and the effect of roughness on fluid hydrodynamics for different cross-sectional geometries. The differences in the uncharacteristic behavior of the transport mechanisms through microchannels due to compressibility and rarefaction, relative roughness, property variations and viscous dissipation effects are discussed. Finally, progress on recent development of micromixers has been reported for different micromixer types and designs. The micromixers have been quantified based on their operating ranges (in terms of characteristic dimensionless numbers such as Reynolds number
Re, Peclet number
Pe, and Strouhal number
St) and mixing characteristics.
Biodiesel is eco-friendly, less toxic and one of the most researched biofuels in recent years to reduce our reliance on fossil fuels and minimize emissions. The various problems associated with ...batch-type reactors are longer residence time, higher operating costs, and energy consumption with low production efficiency. Researchers are now focusing on continuous flow biodiesel production techniques to overcome problems in batch reactors. This paper highlights various reactors used in continuous flow biodiesel synthesis, catalyst mechanism, hybrid reactors technique and separation methods. Various continuous flow reactors used in biodiesel production have been discussed and the microreactor was intensively elaborated. Compared to traditional reactors, microreactor technology exhibits higher efficiency, improved mixing, high heat and mass transfer rates due to a high surface-area-to-volume ratio and short diffusion distance. The parameters that influence the liquid-liquid phase flow patterns in the microreactors include mixer type, channel size, internal configuration reaction time, reaction temperature, and alcohol to oil ratio. Post-treatment techniques help to improve the quality of the biodiesel and utilization of by-products has been discussed. The limitations and practical implications prevailing in the microreactors help improve the reactor techniques forward in large-scale production. Finally, the review addresses future directions in bridging the gap in current research on microreactors for better yield and high biodiesel quality.
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•A review of the various continuous flow reactors used for biodiesel production was presented.•Biodiesel production using continuous-flow microreactors and their significance was intensively discussed.•Advances required to improve the improve mass transfer rate and conversion of biodiesel was presented.•The importance of the post-treatment techniques to improve the quality of biodiesel was briefly discussed.
Nowadays, lipid nanoparticles have gained profound interest in chemical and biomedical engineering. The rapid development of therapeutic nanosystems has led to a need to design suitable approaches to ...synthesize bio-carriers for efficient drug delivery. Microfluidic methods provide an excellent opportunity to acquire desirable nanoparticle properties, including stability, size, shape, and size distribution, which are often challenging to obtain using conventional bulk synthesis methods. Rapid mixing is a crucial factor in the nanoprecipitation process as it influences the size and size distribution of the nanoparticles. Within this regard, in this work, we report an ultrafast acoustofluidic micromixer to synthesize liposome nanoparticles, which have been widely investigated in the literature as drug carriers due to their biocompatibility and biodegradability. This research has also investigated the influence of glycerol addition to the solvent to control the size of the liposomes. Our findings indicate that utilizing the acoustofluidic platform resulted in the production of nanoscale liposomes with small mean sizes compared to the hydrodynamic flow-focusing (HFF) method. Furthermore, the inclusion of glycerol led to a significant reduction in liposome size. These results emphasize the potential of the proposed approach for the efficient and precise synthesis of liposome nanoparticles with improved characteristics, which can be utilized in various biomedical and drug delivery applications.
•A co-flow-focusing structured micromixer was proposed to change the initial distribution inside the newly formed droplet, fully utilizing the flow field to enhance mixing.•The evolution of droplet ...mixing dynamics during the droplet generation and movement process was investigated.•A multiphysics field model was established to characterize the droplet generation and mixing.•The pre-mixing effect, which influences the initial mixing efficiency, was found during the droplet generation process.
The droplet-based micromixing technology has been widely used in chemical synthesis, biomonitoring, and other fields due to its good mass transfer performance. Compared with plug-shaped droplets, spherical droplets have higher productivity and better mass transfer performance. However, the traditional mixing intensification method cannot effectively break the vortex symmetry inside the droplets at the changes of the channel structure, limiting the mixing performance of spherical droplets. This study proposed a co-flow-focusing structure to realize mixing enhancement by changing the initial distribution of internal components of newly formed droplets. A full-cycle multiphysics field model from droplet generation to mixing and exiting was developed to further reveal the evolution of droplet mixing dynamics based on internal vortices. The effects of the dispersed phase flow rate Qd, the continuous phase flow rate Qc, and the local geometry on the mixing performance were investigated. The results show that high initial mixing efficiency and internal vortex strength both can enhance mixing. There exists a critical dispersed phase flow rate Qd* leading to the lowest mixing rate. Conversely, increasing Qc enhances the initial mixing efficiency and internal vortex strength. The final mixing efficiency within the droplet (t = 50 ms) was increased by 15 % when Qc was varied from 2.20 μL/min to 5.04 μL/min. Additionally, the contraction orifice further enhances the mixing performance of the co-flow-focusing structure. The structure proposed in this paper simplifies the design of droplet-based micromixers, and the findings contribute to the further development of the co-flow-focusing structured droplet-based micromixer.
•3D printed rapid and inexpensive multi-bore micromixer fabrication.•Simple architectures numerically evaluated with CFD and experimentally validated with RTD.•Strong link between sharp bends and ...enhanced radial dispersion at low Dm.•High-performance microreactors suited for immobilised (bio)catalytic reactions.
Microreactors offer large surface-area-to-volume (SAV) ratios and short diffusion distances, yet, even at sub-millimetre space, there remains a level of mass transfer control of reactions. This can be minimised using passive micromixers currently requiring access to advanced microfabrication techniques. We report the fast fabrication and in-depth micromixing characterisation of inexpensive non-linear microstructure prototypes using, for the first time, a flexible fluoropolymer microcapillary film (MCF) re-shaped, post-extrusion, with 3D printed templates offering in-flow enhancement of mass transfer in immobilised (bio)catalytic reactions not previously studied for this type of micro-engineered material. The versatile “push-and-click” 3D printed templates allow one-step production of multi-bored, non-invasive micromixers with simple architectures, namely ‘square’, ‘zigzag’ and ‘wavy’ geometries without the limitations of conventional microfluidic devices. The passive micromixers were numerically evaluated using Computational Fluid Dynamics (CFDs) and extensively validated experimentally using novel Residence time distribution (RTD) data which assessed the role of Reynold numbers (0.6 – 60) and molecular diffusion coefficients (10−6 –10−11 m2/s), providing significant in-depth understanding of fluid flow distribution. By evaluating the in-flow oxidative coupling reaction of o-phenylenediamine (OPD, a chromogenic substrate) to 2,3-diaminophenazine (DAP) with an immobilised enzyme, horseradish peroxidase (HRP), we demonstrated the reaction rates in the ‘square’ and ‘zigzag’ (sharp bends) were improved by ∼43 and ∼46% respectively, compared to straight microcapillaries. This is linked to enhanced radial fluid movement. The proposed prototypes can be readily tailored for facilitated fabrication of practical high-performance microreactors suited for heterogeneous assays or in-flow (bio)catalytic reactions in non-microdevice dedicated labs.
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